Fuel injection control apparatus

ABSTRACT

A fuel injection control apparatus including a microprocessor. The microprocessor is configured to perform calculating a target injection time, determining a first crank angle defining a start of fuel injection and a second crank angle defining an end of fuel injection, controlling a fuel injector in an injection start priority mode in which the fuel is injected for the first target injection time from a first time point corresponding to the first crank angle or an injection end priority mode in which the fuel is injected for the second target injection time from a second time point corresponding to a target crank angle, and the controlling including controlling the fuel injector so as to inject the fuel in the injection start priority mode or the injection end priority mode in accordance with an injection mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2020-065397 filed on Mar. 31, 2020, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a fuel injection control apparatus forcontrolling an injection timing of a fuel in a direct-injection internalcombustion engine.

Description of the Related Art

As this type of apparatuses, there have been known apparatuses thatcontrol the energization of an injector using a step-up voltagegenerated by a booster so that the injector injects fuel in the targetamount. Such an apparatus is described in, for example, JapaneseUnexamined Patent Publication No. 2020-016154 (JP2020-016154A). Theapparatus of JP2020-016154A controls the injection timing so that thenext injection is started at a predetermined interval after an injectorstarts to inject fuel.

However, the injection time for injecting the fuel in the target amountmay vary with changes in the pressure, temperature, or the like of thefuel. For this reason, in the case of apparatuses that inject fuel whilecontrolling the injection start timing, such as JP2020-016154A, theinjection end time point may be delayed, resulting in an adverse effecton the combustion performance.

SUMMARY OF THE INVENTION

An aspect of the present invention is a fuel injection control apparatusfor an internal combustion engine, the internal combustion engineincluding a piston reciprocating in a cylinder and a fuel injectorarranged to inject a fuel into a combustion chamber facing the piston inthe cylinder. The apparatus includes an air amount detector configuredto detect an amount of an air flowing into the cylinder or a physicalquantity having a correlation with the amount of the air, and anelectronic control unit having a microprocessor and a memory. Themicroprocessor is configured to perform: calculating a target injectiontime of the fuel including a first target injection time and a secondtarget injection time, based on the amount of the air or the physicalquantity detected by the air amount detector; determining a first crankangle at which a fuel injection by the fuel injector is to be startedand a second crank angle at which the fuel injection is to be ended;controlling the fuel injector so as to inject the fuel in an injectionstart priority mode in which the fuel is injected for the first targetinjection time from a first time point corresponding to the first crankangle or an injection end priority mode in which the fuel is injectedfor the second target injection time from a second time pointcorresponding to a target crank angle, the target crank angle beingobtained by decreasing a crank angle range corresponding to the secondtarget injection time from the second crank angle; and switching aninjection mode to one of a plurality of injection modes in accordancewith an operating state of the internal combustion engine, an injectionfrequency and an injection timing being determined in accordance witheach of the plurality of injection modes, and wherein the microprocessoris configured to perform the controlling including controlling the fuelinjector so as to inject the fuel in the injection frequency and theinjection timing in accordance with the injection mode, and furtherinject the fuel in the injection start priority mode or the injectionend priority mode in accordance with the injection mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, and advantages of the present invention willbecome clearer from the following description of embodiments in relationto the attached drawings, in which:

FIG. 1 is a drawing schematically showing the configuration of a traveldrive unit of a hybrid vehicle including an internal combustion engineto which a fuel injection control apparatus according to an embodimentof the present invention is applied;

FIG. 2 is a drawing schematically showing a configuration of maincomponents of an engine of FIG. 1;

FIG. 3 is a block diagram showing the configuration of main componentsof an internal combustion engine control apparatus to which the fuelinjection control apparatus according to the embodiment of the presentinvention is applied;

FIG. 4 is a diagram showing an example of switching of injection modesin the internal combustion engine control apparatus of FIG. 3;

FIG. 5 is a diagram showing an example of an injection map correspondingto an adherence reduction mode of FIG. 4;

FIG. 6 is a block diagram showing a functional configuration of a statedetermination unit of FIG. 3;

FIG. 7 is a flowchart showing an example of a process performed by acontroller in FIG. 3;

FIG. 8 is a block diagram showing a main configuration of the fuelinjection control apparatus according to the embodiment of theinvention;

FIG. 9 is a diagram showing a flow of power supplied to an injector ofFIG. 8;

FIG. 10A is a diagram showing an example of an injection patter of fuelin an injection start priority mode by the fuel injection controlapparatus according to the embodiment of the invention;

FIG. 10B is a diagram showing an example of an injection patter of fuelin an injection end priority mode by the fuel injection controlapparatus according to the embodiment of the invention; and

FIG. 11 is a flowchart showing an example of a process performed by acontroller in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be describedwith reference to FIGS. 1 to 11. A fuel injection control apparatusaccording to the embodiment of the present invention is applied tovehicles including a direct-injection gasoline engine as an internalcombustion engine. Specifically, this fuel injection control apparatusis applied to engine vehicles that travel using only an engine as adrive source and hybrid vehicles that travel using an engine and a motoras drive sources. Hereafter, an example will be described in which thisfuel injection control apparatus is applied to a hybrid vehicle.

FIG. 1 is a drawing schematically showing the configuration of thetravel drive unit of the hybrid vehicle including the internalcombustion engine, i.e., the engine to which the fuel injection controlapparatus according to the embodiment of the present invention isapplied. As shown in FIG. 1, a first motor-generator (MG1) 2 isconnected to the output shaft 1 a of an engine (ENG) 1, and a secondmotor-generator (MG2) 3 is connected to the rotation shaft 4 a of adrive wheel 4. The first motor-generator 2 mainly serves as a generatorthat generates power when driven by the engine 1, and the powergenerated by the first motor-generator 2 is accumulated in a battery(BAT) 5 through an inverter (not shown). The second motor-generator 3mainly serves as a travel motor that is driven by power supplied fromthe battery 5 through an inverter (not shown).

A clutch 6 is interposed between the output shaft 1 a of the engine 1and the rotation shaft 4 a of the drive wheel 4, and the output shaft 1a and rotation shaft 4 a are connected or disconnected through theclutch 6. When the output shaft 1 a and rotation shaft 4 a aredisconnected, the vehicle travels by only the power of the secondmotor-generator 3 (EV travel). When the output shaft 1 a and rotationshaft 4 a are connected through the clutch 6, the vehicle travels byonly the power of the engine 1 (engine travel) or travels by the powerof the engine 1 and second motor-generator 3 (hybrid travel). In otherwords, the vehicle is able to switch the travel mode among an EV mode,in which EV travel is performed, an engine mode, in which engine travelis performed, and a hybrid mode, in which hybrid travel is performed.

FIG. 2 is a drawing schematically showing the configuration of maincomponents of the engine 1. The engine 1 is a spark-ignition internalcombustion engine having a fuel cut function of stopping supply of fuelto multiple cylinders during deceleration or the like of the vehicle andis a four-stroke engine, which goes through four strokes consisting ofintake, compression, expansion and exhaust in one operation cycle. Forconvenience, the operation from the start of the intake stroke to theend of the exhaust stroke is referred to as “one cycle of the combustionof the engine,” or simply as “one cycle.” Although the engine 1 includesmultiple cylinders, such as four, six, or eight ones, the configurationof one cylinder is shown in FIG. 2. The cylinders have the sameconfiguration.

As shown in FIG. 2, the engine 1 includes a cylinder 102 formed in acylinder block 101, a piston 103 disposed slidably in the cylinder 102,and a combustion chamber 105 formed between the crown surface 103 a ofthe piston 103 (piston crown surface) and a cylinder head 104. Forexample, a recess 103 b is formed in the piston crown surface 103 a soas to be along a tumble flow in the cylinder. The piston 103 isconnected to a crankshaft 107 through a connecting rod 106 and rotatesthe crankshaft 107 (corresponding to the output shaft 1 a of FIG. 1) byreciprocating of the piston 103 along the inner wall of the cylinder102.

The cylinder head 104 is provided with an intake port 111 and an exhaustport 112. An intake passage 113 communicates with the combustion chamber105 through the intake port 111, while an exhaust passage 114communicates with the combustion chamber 105 through the exhaust port112. The intake port 111 is opened and closed by an intake valve 115,and the exhaust port 112 is opened and closed by an exhaust valve 116. Athrottle valve 119 is disposed on the upstream side of the intakepassage 113 connected to the intake valve 115. The throttle valve 119consists of, for example, a butterfly valve, and the amount of intakeair supplied to the combustion chamber 105 is controlled by the throttlevalve 119. The intake valve 115 and exhaust valve 116 are open and closedriven by a valve train 120.

An ignition plug 11 and a direct-injection injector 12 are mounted onthe cylinder head 104 so as to face the combustion chamber 105. Theignition plug 11 is disposed between the intake port 111 and exhaustport 112 and ignites a fuel-air mixture in the combustion chamber 105 byproducing a spark by electrical energy.

The injector 12 is disposed near the intake valve 115. The injector 12includes a drive portion such as an electromagnetic actuator and piezoactuator, and injects fuel when driven by electrical energy. Morespecifically, the high-pressure fuel is supplied from a fuel tank to theinjector 12 through a fuel pump, and the injector 12 converts the fuelinto high fine particles and injects the resulting fuel into thecombustion chamber 105 obliquely downward at a predetermined timing. Theinjector 12 may be disposed otherwise and may be disposed, for example,near the ignition plug 11.

The valve train 120 includes an intake cam shaft 121 and an exhaust camshaft 122. The intake cam shaft 121 integrally includes intake cams 121a corresponding to the cylinders (cylinders 102), and the exhaust camshaft 122 integrally includes exhaust cams 122 a corresponding to thecylinders. The intake cam shaft 121 and exhaust cam shaft 122 areconnected to the crankshaft 107 through timing belts (not shown) androtate once each time the crankshaft 107 rotates twice.

The intake valve 115 is opened and closed by rotation of the intake camshaft 121 through an intake rocker arm (not shown) at a predeterminedtiming corresponding to the profile of the intake cam 121 a. The exhaustvalve 116 is opened and closed by rotation of the exhaust cam shaft 122through an exhaust rocker arm (not shown) at a predetermined timingcorresponding to the profile of the exhaust cam 122 a.

A catalyst device 13 for purifying exhaust gas is disposed on theexhaust passage 114. The catalyst device 13 is a device including athree-way catalyst having a function of removing and purifying HC, CO,and NOx contained in exhaust gas by oxidation and reduction. Other typesof catalyst, such as an oxidation catalyst that oxidizes CO and HC inexhaust gas, may be used. When the temperature of the catalyst includedin the catalyst device 13 is increased, the catalyst is activated,resulting in an increase in the exhaust gas purification effect of thecatalyst device 13.

To improve fuel efficiency, the engine 1 has a fuel cut function ofstopping fuel injection from the injector 12 when predetermined fuel cutconditions are satisfied during engine travel. That is, when the fuelcut conditions are satisfied, the mode is switched (referred to as the“F/C mode”) and thus fuel injection is stopped. For example, the fuelcut conditions are as follows: the manipulated variable of theaccelerator pedal (accelerator opening) is equal to or smaller than apredetermined value; the rotational speed of the crankshaft 107 (enginespeed) is equal to or greater than a predetermined value; and thevehicle speed is equal to or greater than a predetermined value. Thesefuel cut conditions are satisfied, for example, during decelerationtravel. In the F/C mode, intake of air into the combustion chamber 105is continued.

Also, to improve fuel efficiency, the engine 1 has an idling stopfunction of stopping fuel injection from the injector 12 whenpredetermined idling stop conditions are satisfied. Specifically, whenthe idling stop conditions are satisfied, the mode is switched to anidling stop mode (referred to as the “I/S mode”) and thus fuel injectionis stopped. For example, the idling stop conditions are as follows: thevehicle speed is equal to or lower than a predetermined vehicle speedduring a stop or the like of the vehicle; the accelerator pedal is notin operation; and the operation of a brake pedal is detected. In the I/Smode, the engine 1 is stopping, and intake of air into the combustionchamber 105 is stopped, as during EV travel.

Although not shown, the engine 1 includes an exhaust gas recirculatorthat recirculates a part of exhaust gas to an intake system, a blow-bygas return device that returns blow-by gas to the intake system andburns it again, a purge controller that controls supply of evaporativefuel gas in a fuel tank to the intake system, and the like. The exhaustgas recirculator includes an internal EGR that recirculates exhaust gasin the combustion chamber 105 under the control of the valve train 120and an external EGR that guides a part of exhaust gas from the exhaustpassage 114 to the intake system through an EGR passage and an EGRvalve. The purge controller includes a purge passage through whichevaporative fuel gas in the fuel tank is guided to the intake system anda purge valve that is disposed on the purge passage and controls theflow of gas passing through the purge passage. The engine 1 may includea supercharger.

The above engine 1 is controlled by an internal combustion enginecontrol apparatus. FIG. 3 is a block diagram showing the configurationof main components of the internal combustion engine control apparatusaccording to the embodiment of the present invention. As shown in FIG.3, the internal combustion engine control apparatus is formed centeredon a controller 30 for controlling the engine and includes various typesof sensors, actuators, and the like connected to the controller 30.Specifically, a crank angle sensor 31, an accelerator opening sensor 32,a water temperature sensor 33, an intake air amount sensor 34, an AFsensor 35, the ignition plug 11, and the injector 12 are connected tothe controller 30.

The crank angle sensor 31 is disposed on the crankshaft 107 andconfigured to output pulse signals in association with rotation of thecrankshaft 107. More specifically, the crank angle sensor 31 outputpulse signals every time the crank shaft 10 rotates by a predeterminedangle (e.g., 30°). The controller 30 identifies the rotation angle ofthe crankshaft 107 (crank angle) with respect to the position of the topdead center (TDC) of the piston 103 at the start of the intake strokeand calculates the engine RPM (engine speed) on the basis of pulsesignals from the crank angle sensor 31.

The accelerator opening sensor 32 is disposed on the acceleration pedal(not shown) of the vehicle and detects the manipulated variable of theacceleration pedal (accelerator opening). A command indicating thetarget torque of the engine 1 is issued on the basis of the valuedetected by the accelerator opening sensor 32. The water temperaturesensor 33 is disposed on a passage through which engine cooling waterfor cooling the engine 1 flows and detects the temperature of the enginecooling water (cooling water temperature). The intake air amount sensor34 is a sensor that detects the amount of intake air and consists of,for example, an air flow meter disposed on the intake passage 113 (morespecifically, on the upstream side of the throttle valve). The AF sensor35 is disposed on the exhaust passage 114 and on the upstream side ofthe catalyst device 13 and detects the air-fuel ratio of exhaust gas inthe exhaust passage 114. Although not shown, a variety of sensors suchas an intake air pressure sensor, atmospheric pressure sensor and intakeair temperature other than the above sensors are connected to thecontroller 30.

The controller 30 consists of an electronic control unit (ECU) andincludes a computer including an arithmetic processing unit, such as aCPU, a storage unit, such as a ROM or RAM, and other peripheralcircuits. The controller 30 includes, as functional elements, aninjection mode switching unit 301, a temperature information acquisitionunit 302, a state determination unit 303, an ignition control unit 304,and an injector control unit 305.

The injection mode switching unit 301 switches the injection mode inaccordance with the operation state of the engine 1. FIG. 4 is a diagramshowing an example of switching of the injection mode in the period fromwhen the operation of the engine 1 is started in response to turn-on ofan ignition switch until the operation of the engine 1 is ended inresponse to turn-off of the ignition switch. As shown in FIG. 4, theinjection mode includes a start mode M1, a catalyst warm-up mode M2, anadherence reduction mode M3, a homogeneity improvement mode M4, a knocksuppression mode M5, and a fuel stop mode M6. The homogeneityimprovement mode M4 and knock suppression mode M5 represent highin-cylinder temperature states, in which the piston temperature(in-cylinder temperature) is high, and are collectively referred to asthe “high in-cylinder temperature mode M7.”

In the modes M1 to M5 other than the fuel stop mode in FIG. 4, the crankangle in a range from the start of the intake stroke (the intake topdead center (TDC)) to the end of the compression stroke (the compressiontop dead center (TDC)) is represented by the angle of a clockwise circleusing the intake top dead center (TDC) as the start point, and the fuelinjection timing is represented by a hatched sector extending radiallyfrom the center of the circle. In the intake stroke, the crank angle isin a range equal to or greater than 0° and equal to or smaller than180°; in the compression stroke, the crank angle is in a range equal toor greater than 180° and equal to or smaller than 360. Hereafter, acrank angle range from 0° to 90° may be referred to as the first half ofthe intake stroke, a crank angle range from 90° to 180° as the secondhalf of the intake stroke, a crank angle range from 180° to 270° as thefirst half of the compression stroke, and a crank angle range from 270°to 360° as the second half of the compression stroke.

The start mode M1 is a mode for starting the engine 1 and is performedimmediately after the ignition switch is turned on, or when the mode isrestored from the EV mode or I/S mode. In the start mode M1, the engine1 is cranked and then a mixture is produced by injecting the fuel twicein the first half of the compression stroke, that is, by two-injectioncompression, as shown in FIG. 4. In this case, the same amount of fuelis injected each time. By injecting the fuel in the compression stroke,the startability of the engine 1 is improved. Also, by injecting thefuel multiple times (in multiple stages) in the first half of thecompression stroke, the amount of each fuel injection is suppressed.This allows for suppressing adherence of the fuel to the piston crownsurface 103 a or the wall surface of the cylinder 102 and thussuppressing soot formation.

As long as both an improvement in the startability and suppression ofsoot are achieved, the start mode M1 is not limited to two-injectioncompression and may be an injection in a different injection pattern,such as one in which the fuel is injected once in the compression stroke(one-injection compression) or one in which the fuel is injectedmultiple times in the intake stroke and compression stroke(multiple-injection intake-compression). When the start mode M1 iscomplete, the injection mode is switched to one of the catalyst warm-upmode M2, adherence reduction mode M3, and high in-cylinder temperaturemode M7 (e.g., homogeneity improvement mode M4).

The catalyst warm-up mode M2 is a mode for promoting warm-up of thecatalyst device 13 to activate the catalyst earlier. In the catalystwarm-up mode M2, a mixture is produced by injecting the fuel twice inthe intake stroke, that is, by two-injection intake, as shown in FIG. 4.In this case, the same amount of fuel is injected each time. Also, inthe catalyst warm-up mode M2, the timing at which the mixture is ignitedby the ignition plug 11 is retarded from the MBT (minimum advance forthe best torque), at which the best torque is obtained. The retardationof the ignition timing causes the mixture to be burnt later and thusincreases the amount of air supplied to the combustion chamber 105 forgenerating the target torque and the amount of fuel injection. Thisincreases the amount of heat generated by combustion of the mixture andthus warms up the catalyst device 13 earlier. In the catalyst warm-upmode M2, the fuel is injected at a predetermined timing that ispreviously stored in the memory and that is not changed in accordancewith the engine RPM (engine speed) or the amount of intake air.

By injecting the fuel by two-injection intake in the catalyst warm-upmode M2, the mixture is homogenized, resulting in an increase in thecombustion efficiency and suppression of emission deterioration. As longas emission deterioration is suppressed, the catalyst warm-up mode M2 isnot limited to two-injection intake and may be an injection in adifferent injection pattern, such as one in which the fuel is injectedonce in the intake stroke (one-injection intake) or one in which thefuel is injected multiple times in the intake stroke and compressionstroke (multiple-injection intake-compression). When the catalystwarm-up mode M2 is complete, the injection mode is switched to theadherence reduction mode M3 or high in-cylinder temperature mode M7(e.g., homogeneity improvement mode M4).

The adherence reduction mode M3 is performed in order to reduce sootwhen the piston temperature is low. In the adherence reduction mode M3,the fuel is injected in an area other than a predeterminedinjection-prohibited area near the intake top dead center (TDC) at thestart of the intake stroke and a predetermined injection-prohibited areanear the compression top dead center (TDC) at the end of the compressionstroke, that is, in an area in which the piston crown surface 103 a isaway from the injector 12 (injectable areas). For example, theinjection-prohibited area is set in a part or almost all of the firsthalf of the intake stroke and a part or almost all of the second half ofthe compression stroke.

More specifically, the injection-prohibited area is set in accordancewith the engine speed. As the engine speed becomes higher, the pistoncrown surface 103 a retreats from the injector 12 in the intake strokeat a higher speed and approaches the injector 12 in the compressionstroke at a higher speed. For this reason, as the engine speed becomeshigher, the injection-prohibited area in the intake stroke becomesnarrower (the end of the injection-prohibited area is shifted to theadvance side), and the injection-prohibited area in the compressionstroke becomes wider (the start of the injection-prohibited area isshifted to the retard side).

The fuel injection frequency and fuel injection timing in the injectablearea are determined on the basis of a map previously stored in thememory, for example, a map shown in FIG. 5. Specifically, as shown inFIG. 5, the injection frequency and injection timing are determined onthe basis of a predetermined map so as to be associated with acharacteristic f1 of the maximum output torque corresponding to theengine speed Ne and the target amount of injection Q, as shown in FIG.5, and the injection frequency is set to one to four times. If theinjection frequency is multiple times, the same amount of fuel isinjected each time. The target amount of injection Q is calculated as avalue such that the actual air-fuel ratio becomes the target air-fuelratio and is determined in accordance with the amount of intake air. Forthis reason, the map of FIG. 5 may be rewritten as a map of the enginespeed Ne and the amount of intake air G, like the map of the homogeneityimprovement mode M4 of FIG. 4.

To suppress adherence of the fuel to the piston crown surface 103 a, itis preferred to reduce the amount of one injection by increasing theinjection frequency. However, the minimum amount of one injection Qminof the injector 12 is defined by the specification of the injector 12,and the injector 12 cannot inject the fuel in a smaller amount than theminimum amount of injection Qmin (MinQ constraint). Accordingly, theinjection frequency is once in an area in which the target amount ofinjection is small, and is gradually increased to twice, three times,and four times as the target amount of injection Q is increased.

On the other hand, to increase the injection frequency, the injector 12has to be driven at a higher speed. For this reason, for example, acapacitor in an injector driving electrical circuit of the controller 30has to be repeatedly charged and discharged within a short time. In thiscase, the injector 12 has to be driven at a higher speed as the enginespeed Ne becomes higher. Thus, the controller 30 bears a higherelectrical load and generates a greater amount of heat. The injectionfrequency is limited due to this heat constraint of the controller 30(ECU heat constraint). That is, while the injection frequency is fourtimes in an area in which the engine speed Ne is low, the injectionfrequency is gradually limited to three times, twice, and once as theengine speed Ne is increased.

In view of the foregoing, for example, the injection frequency is set tofour times (four-stage injection) in an area AR1 in which the enginespeed Ne is smaller than a predetermined value N1 and the target amountof injection Q is equal to or greater than a predetermined value Q3; theinjection frequency is set to three times (three-stage injection) in anarea AR2 in which the engine speed Ne is smaller than a predeterminedvalue N2 and the target amount of injection Q is equal to or greaterthan a predetermined value Q2, except for the area AR1; the injectionfrequency is set to twice (two-stage injection) in an area AR3 in whichthe engine speed Ne is smaller than a predetermined value N3 and thetarget amount of injection Q is equal to or greater than a predeterminedvalue Q1, except for the areas AR1 and AR2; and the injection frequencyis set to once (single injection) in an area AR4 in which the enginespeed Ne is equal to or greater than the predetermined value N3 or thetarget amount of injection Q is smaller than the predetermined value Q1.

The predetermined values N1 to N3 have a relationship of N1<N2<N3, andthe predetermined values Q1 to Q3 have a relationship of Q1<Q2<Q3. Thepredetermined values N1 to N3 and Q1 to Q3 are previously determinedthrough an experiment and stored in the memory. The maximum injectionfrequency in the adherence reduction mode M3 is determined on the basisof the specification of the injector 12, controller 30, or the like, themounting position of the injector 12, or the like and may be smaller orgreater than four times. When the adherence reduction mode is complete,the injection mode is switched to the high in-cylinder temperature modeM7 (e.g., homogeneity improvement mode M4) or fuel stop mode M6.

The homogeneity improvement mode M4 is an injection mode in which fuelefficiency is optimized. In the homogeneity improvement mode, the fuelis injected by one-injection intake or two-injection intake inaccordance with a control map corresponding to the engine speed Ne andthe amount of intake air G previously stored in the memory.Specifically, as shown in FIG. 4, the fuel is injected by two-injectionintake in a high-load, low-rotation area in which the engine speed Ne islow and the amount of intake air G is large, while the fuel is injectedby one-injection intake in an area in which the engine speed Ne is highor the amount of intake air G is small. This control map is changed inaccordance with the cooling water temperature. In the case oftwo-injection intake, the same amount of fuel is injected each time. Byinjecting the fuel by one-injection intake or two-injection intake inthe homogeneity improvement mode, the mixture in the combustion chamber105 is homogenized by a tumble flow and thus fuel efficiency isincreased.

Also, in the homogeneity improvement mode M4, the ignition timing of theignition plug 11 is controlled mainly in accordance with the enginespeed Ne and the amount of intake air G. Specifically, in an area inwhich knocks do not occur or are less likely to occur, the ignitiontiming is controlled to the optimum ignition timing, i.e., MBT that iscloser to the advance side than the compression top dead center (TDC)and that is previously stored in the memory. On the other hand, in anarea in which knocks occur or are more likely to occur, for example, ina high-load, low-rotation area in which the engine speed is low and theamount of intake air is large, the ignition timing is retarded from theMBT in accordance with a characteristic previously stored in the memoryin order to suppress knocks. The ignition timing may be retarded bydisposing a knock sensor that detects knocks and detecting knocks usingthe knock sensor. When predetermined knock suppression conditions aresatisfied, the homogeneity improvement mode M4 is switched to the knocksuppression mode M5.

The knock suppression mode M5 is an injection mode in which knocks aresuppressed. In the knock suppression mode M5, the retarded ignitiontiming is returned (advanced) to the MBT side, and the fuel is injectedonce in the intake stroke (e.g., in the first half of the intake stroke)and once in the compression stroke (e.g., in the first half of thecompression stroke) (multiple-injection intake-compression). In thecompression stroke, the amount of injection is the minimum amount ofinjection Qmin; in the intake stroke, the amount of injection is anamount obtained by subtracting the minimum amount of injection Qmin fromthe target amount of injection Q. By injecting the fuel in thecompression stroke, the temperature of end gas in the combustion chamber105 is reduced by the latent heat of vaporization.

Thus, knocks are suppressed while the amount of retardation of theignition timing is suppressed. As a result, fuel efficiency is increasedcompared to when the ignition timing is retarded and the fuel isinjected only in the intake stroke. When the knock suppression node iscomplete, that is, when the knock suppression conditions becomeunsatisfied, the injection mode is switched to the homogeneityimprovement mode. That is, when the in-cylinder temperature is high (theinjection mode is the high in-cylinder temperature mode M7), theinjection mode is switched between the homogeneity improvement mode M4and knock suppression mode M5 in accordance with whether the knocksuppression conditions are satisfied.

The fuel stop mode M6 is a mode in which fuel injection is stopped andthus combustion is stopped in the combustion chamber 105. When thetravel mode is the EV mode, F/C mode, or I/S mode, the injection mode isswitched to the fuel stop mode M6. For example, when combustion isstopped in the adherence reduction mode M3 or high in-cylindertemperature mode M7, the injection mode is switched to the fuel stopmode M6. When the fuel stop mode M6 is complete, the injection mode isswitched to one of the start mode M1, adherence reduction mode M3, andhigh in-cylinder temperature mode M7.

The temperature information acquisition unit 302 of FIG. 3 acquiresinformation on the temperature in the cylinder 102. This temperatureinformation is information on the in-cylinder temperature, whichinfluences adherence of the fuel in the cylinder 102, and corresponds tothe temperature of the piston crown surface 103 a. For this reason, if asensor capable of accurately detecting the temperature of the pistoncrown surface 103 a is disposed, the temperature information acquisitionunit 302 would only have to acquire information from that sensor.However, the piston crown surface 103 a reciprocates in the cylinder 102so as to face the combustion chamber 105 having a high temperature andtherefore it is difficult to directly accurately detect the temperatureof the piston crown surface 103 a using such a sensor.

On the other hand, the temperature of the piston crown surface 103 a hasa correlation with the amount of intake air G supplied into thecombustion chamber 105 for combustion in the combustion chamber 105.Specifically, when the cumulative amount of the amounts of intake air Gis increased, a larger amount of heat is generated in the combustionchamber 105 and thus the temperature of the piston crown surface 103 acorresponding to the in-cylinder temperature is increased. For thisreason, the temperature information acquisition unit 302 acquiressignals from the intake air amount sensor 34 and calculates thecumulative amount of the amounts of intake air G on the basis of theacquired signals.

The state determination unit 303 determines the operation state of theengine 1 related to switching of the injection mode. FIG. 6 is a blockdiagram showing the functional elements of the state determination unit303. As shown in FIG. 6, the state determination unit 303 includes astart determination unit 303A, a catalyst warm-up determination unit303B, an in-cylinder temperature determination unit 303C, a knockdetermination unit 303D, and a fuel cut determination unit 303E.

In the start mode M1 of FIG. 4, the start determination unit 303Adetermines whether the start of the engine 1 is complete. Specifically,the start determination unit 303A determines whether the start of theengine 1 is complete, on the basis of whether a predetermined countvalue has been counted after the rotational speed of the cranked enginecalculated on the basis of signals from the crank angle sensor 31 isincreased to the complete explosion rotational speed, at which theengine is able to maintain rotation on its own. If the startdetermination unit 303A determines that the start of the engine 1 iscomplete, the injection mode switching unit 301 switches the injectionmode from the start mode M1 to the catalyst warm-up mode M2, adherencereduction mode M3, or high in-cylinder temperature mode M7 (e.g.,homogeneity improvement mode M4).

The start determination unit 303A determines not only whether the startof the engine 1 is complete, but also whether the engine 1 needs to bestarted. Specifically, in the fuel stop mode M6 of FIG. 4, the startdetermination unit 303A determines whether the travel mode needs to beswitched from the EV mode to the engine mode or hybrid mode and whetherthe travel mode needs to be restored from the I/S mode. If the startdetermination unit 303A determines that the travel mode needs to beswitched to the engine mode or that the travel mode needs to be restoredfrom the I/S mode, the injection mode switching unit 301 switches theinjection mode from the fuel stop mode M6 to the start mode M1.

In the catalyst warm-up mode M2 of FIG. 4, the catalyst warm-updetermination unit 303B determines whether warm-up of the catalystdevice 13 (catalyst warm-up) is complete. This determination is adetermination as to whether the total workload of the engine 1 hasreached the target total workload required for catalyst warm-up. Thetarget total workload is set in accordance with the cooling watertemperature detected by the water temperature sensor 33 at the start ofthe engine 1 using a previously stored relational expression,characteristic, or map. For example, when the cooling water temperatureis low, it takes time to warm up the catalyst, since the engine 1 hasyet to be warmed up. In view of the foregoing, the target total workloadis set to a larger value as the cooling water temperature is lower.

The catalyst warm-up determination unit 303B first calculates the totalworkload of the engine 1 corresponding to the cooling water temperatureon the basis of signals from the water temperature sensor 33.Subsequently, when the total workload reaches the target total workload,the catalyst warm-up determination unit 303B determines that thecatalyst warm-up is complete. Thus, the injection mode switching unit301 switches the injection mode from the catalyst warm-up mode M2 to theadherence reduction mode M3 or high in-cylinder temperature mode M7(e.g., homogeneity improvement mode M4).

Also, in the start mode M1 of FIG. 4, the catalyst warm-up determinationunit 303B determines whether catalyst warm-up is needed. For example,when the cooling water temperature is high due to restoration from theEV travel, or the like, the catalyst warm-up determination unit 303Bsets the target total workload to 0 and determines that catalyst warm-upis not needed. In this case, the injection mode switching unit 301switches the injection mode from the start mode M1 to the adherencereduction mode M3 or high in-cylinder temperature mode M7 (e.g.,homogeneity improvement mode M4). On the other hand, if, in the startmode M1, the catalyst warm-up determination unit 303B sets the targettotal workload to a value greater than 0 and determines that catalystwarm-up is needed, the injection mode switching unit 301 switches theinjection mode from the start mode M1 to the catalyst warm-up mode M2.

The in-cylinder temperature determination unit 303C determines whetherthe in-cylinder temperature corresponding to the temperature of thepiston crown surface 103 a is equal to or greater than a predeterminedvalue (e.g., 100° C.), on the basis of the cumulative amount of theamounts of intake air G acquired by the temperature informationacquisition unit 302. That is, the in-cylinder temperature determinationunit 303C determines whether the in-cylinder temperature is a highin-cylinder temperature equal to or greater than the predetermined valueor a low in-cylinder temperature smaller than the predetermined value.In each of the start mode M1, catalyst warm-up mode M2, and fuel stopmode M6 of FIG. 4, the in-cylinder temperature determination unit 303Cdetermines whether the in-cylinder temperature is a high in-cylindertemperature.

In the homogeneity improvement mode M4 of FIG. 4, the knockdetermination unit 303D determines whether the knock suppressionconditions are satisfied. This determination is a determination as towhether the amount of retardation of the ignition timing for suppressingknocks has become equal to or greater than a predetermined value and isa determination as to whether the injection mode needs to be switched tothe mode in which knocks are suppressed. When the engine rotationalspeed (engine speed) is high and when the cooling water temperature islow, knocks are less likely to occur. From this viewpoint, the knocksuppression conditions are as follows: the amount of retardation of theignition timing from the MBT is equal to or greater than a predeterminedvalue; the cooling water temperature is equal to or greater than apredetermined value; and the engine speed is equal to or smaller than apredetermined value. If the knock determination unit 303D determinesthat the knock suppression conditions are satisfied, the injection modeswitching unit 301 switches the injection mode from the homogeneityimprovement mode M4 to the knock suppression mode M5.

If, in the knock suppression mode M5, the knock determination unit 303Ddetermines that the knock suppression conditions are unsatisfied, theinjection mode switching unit 301 switches the injection mode from theknock suppression mode M5 to the homogeneity improvement mode M4. Theinjection mode may be switched from the adherence reduction mode M3 tothe knock suppression mode M5 without going through the homogeneityimprovement mode M4. Specifically, if, in the adherence reduction modeM3, the in-cylinder temperature determination unit 303C determines thatthe in-cylinder temperature is high, the injection mode may be switchedto the knock suppression mode M5.

The fuel cut determination unit 303E determines whether fuel cut isneeded in each of the catalyst warm-up mode M2, adherence reduction modeM3, and high in-cylinder temperature mode M7 of FIG. 4. In other words,the fuel cut determination unit 303E determines whether the travel modeneeds to be switched to the EV mode, F/C mode, or I/S mode. If the fuelcut determination unit 303E determines that fuel cut is needed, theinjection mode switching unit 301 switches the injection mode from thecatalyst warm-up mode M2, adherence reduction mode M3, or highin-cylinder temperature mode M7 to the fuel stop mode M6.

The ignition control unit 304 of FIG. 3 outputs control signals to theignition plug 11 so that the ignition timing becomes the target ignitiontiming according to a map or characteristic corresponding to theoperation state previously stored in the memory. For example, in thecatalyst warm-up mode M2, the ignition control unit 304 outputs controlsignals to the ignition plug 11 so that the ignition timing is retardedfrom the MBT. In the homogeneity improvement mode M4, the ignitioncontrol unit 304 outputs control signals to the ignition plug 11 so thatthe ignition timing becomes the MBT or is retarded to suppress knocks.In the knock suppression mode M5, the ignition control unit 304 outputscontrol signals to the ignition plug 11 so that the retarded ignitiontiming is returned (advanced) to the MBT side.

The injector control unit 305 calculates the target amount of injectionper cycle in accordance with the amount of intake air detected by theintake air amount sensor 34 while performing feedback control so thatthe actual air-fuel ratio detected by the AF sensor 35 becomes thetarget air-fuel ratio (e.g., a theoretical air-fuel ratio). The injectorcontrol unit 305 then calculates the target amount of one injection (theunit target amount of injection) corresponding to the injection mode ofFIG. 4 and outputs control signals to the injector 12 so that theinjector 12 injects the fuel in the unit target amount at apredetermined timing.

FIG. 7 is a flowchart showing an example of a process performed by thecontroller 30 in accordance with a program previously stored in thememory and, more specifically, an example of a process related toswitching of the injection mode. For example, the process shown in thisflowchart is started when a command to start the engine 1 is issued inresponse to turn-on of the ignition switch, and repeated in apredetermined cycle. FIG. 7 does not show a process related to switchingfrom the fuel stop mode M6 of FIG. 4 to any other injection mode or aprocess related to switching from any other injection mode to the fuelstop mode M6.

As shown in FIG. 7, first, in S1 (5: a process step), the controller 30determines whether a start completion flag is 1. The start completionflag is 0 at the initial time and is set to 1 when the start of theengine 1 is complete in the start mode M1. If the determination in S1 isNO, the process proceeds to S2; if the determination in S1 is YES, theprocess skips S2 to S4 and proceeds to S5. In S2, the injection mode isswitched to the start mode.

Then, in S3, the controller 30 determines whether the start of theengine 1 is complete, that is, whether the engine speed has reached thecomplete explosion speed, on the basis of signals from the crank anglesensor 31. If the determination in S3 is YES, the process proceeds toS4; if the determination in S3 is NO, the process returns to S2. In S4,the controller 30 sets the start completion flag to 1.

Then, in S5, the controller 30 determines whether warm-up of thecatalyst device 13 is needed, on the basis of whether the target totalworkload set on the basis of signals from the water temperature sensor33 is 0. If the determination in S5 is YES, the process proceeds to S6;if the determination in S5 is NO, the process skips S6 and S7 andproceeds to S8. In S6, the controller 30 switches the injection mode tothe catalyst warm-up mode M2. In S7, the controller 30 calculates thetotal workload of the engine 1 on the basis of signals from the intakeair amount sensor 34, as well as determines whether catalyst warm-up iscomplete, on the basis of whether the total workload has reached thetarget total workload. If the determination in S7 is YES, the processproceeds to S8; if the determination in S7 is NO, the process returns toS6.

In S8, the controller 30 determines whether the in-cylinder temperatureis equal to or greater than the predetermined value, that is, whether itis a high in-cylinder temperature, on the basis of the cumulative amountof the amounts of intake air G acquired from the temperature informationacquisition unit 302. If the determination in S8 is YES, the processproceeds to S9 and the controller 30 switches the injection mode to thehigh in-cylinder temperature mode M7.

Then, in S10, the controller 30 determines whether the knock suppressionconditions are satisfied, on the basis of the amount of retardation ofthe ignition timing from the MBT, the cooling water temperature detectedby the water temperature sensor 33, and the engine speed detected by thecrank angle sensor 31. If the determination in S10 is YES, the processproceeds to S11; if the determination in S10 is NO, the process proceedsto S12. In S11, the injection mode is switched to the knock suppressionmode M5; in S12, the injection mode is switched to the homogeneityimprovement mode M4. On the other hand, if the determination in S8 isNO, the process proceeds to S13 and the injection mode is switched tothe adherence reduction mode M3.

The main operation of the above internal combustion engine controlapparatus will be described more specifically. When the ignition switchis turned on, the fuel is injected by two-injection compression and theengine 1 is started (S2). If the cooling water temperature is low due tothe first start of the engine 1, or the like, warm-up of the catalystdevice 13 is needed and the fuel is injected by two-injection intake(S6). Thus, the ignition timing is retarded from the MBT so that themixture is burnt later, allowing the catalyst device 13 to be warmed upearlier.

After the warm-up of the catalyst device 13 is complete (e.g.,immediately after completion of the warm-up following the first start ofthe engine 1), the in-cylinder temperature may have yet to be increasedto a predetermined temperature (e.g., 100° C.) required to reduceadherence of soot to the piston crown surface 103 a. In this case, thefuel is injected in accordance with the map of FIG. 5 in a range fromthe second half of the intake stroke to the first half of compressionstroke so that a reduction in adherence of soot is preferentiallyperformed (S13). Thus, for example, the fuel is injected four times in ahigh-load, low-rotation area AR1. As a result, the amount of one fuelinjection of the injector 12 is reduced and thus adherence of the fuelis effectively suppressed.

On the other hand, if the in-cylinder temperature after completion ofthe warm-up of the catalyst device 13 is equal to or greater than apredetermined temperature, soot is less likely to occur. This is becauseeven if the fuel adheres to the piston crown surface 103 a, the fuelinstantly evaporates. In this case, the fuel is injected in the intakestroke (by two-injection intake or one-injection intake) (S12). Thus,the mixture in the combustion chamber 105 is homogenized, resulting inan increase in the combustion efficiency. The fuel is injected bytwo-injection intake also during catalyst warm-up. However, the abovefuel injection in the intake stroke (at high in-cylinder temperaturestate) is performed at a timing different from that during catalystwarm-up.

If the knock suppression conditions are satisfied when the fuel is beinginjected in the intake stroke in a high in-cylinder temperature state,the fuel is injected in the intake stroke and the fuel of the minimumamount Qmin is also injected in the compression stroke (S11). Thus, thetemperature of the mixture is reduced, resulting in suppression ofknocks. As a result, the amount of retardation of the ignition timingfor suppressing knocks is reduced, and the ignition timing approachesthe MBT. Thus, the combustion efficiency is increased.

When the engine 1 is started due to restoration from the EV mode or I/Smode, or the like, the cooling water temperature may be sufficientlyhigh. In this case, the injection mode is switched to the highin-cylinder temperature mode M7 (e.g., homogeneity improvement mode M4)or adherence reduction mode M3 (S5→S8→S9, S5→S8→S13) without warming upthe catalyst device 13 after the start of the engine. Thus, efficientcombustion is performed after the start of the engine while adherence ofsoot to the piston crown surface 103 a is suppressed.

Given the above configuration, the fuel injection control apparatusaccording to the embodiment of the present invention will be described.To cause the injector 12 to inject the fuel, the injection pattern isdetermined in accordance with the injection mode switched by theinjection mode switching unit 301, as described above. Also, the targetinjection time required to inject the fuel in the target amountcorresponding to the amount of intake air or the like is calculated.Then, control signals are outputted to the injector 12 (to be moreprecise, the driver circuit of the injector 12) so that the fuel isinjected for the target injection time from the target crank angledetermined in accordance with the injection pattern.

However, the crank angle range corresponding to the injection time forinjecting the fuel in the target amount varies with changes in theengine speed or the like. For this reason, if the fuel is alwaysinjected using the injection start time point as a reference, theinjection end time point may be delayed. Thus, soot adherence, emissiondeterioration, or the like may occur and affect the combustionperformance. In view of the foregoing, the fuel injection controlapparatus according to the present embodiment is configured as follows.

FIG. 8 is a block diagram showing the configuration of main componentsof the fuel injection control apparatus according to the presentembodiment. Some elements of this fuel injection control apparatus arethe same as those of the control apparatus of FIG. 3 and are given thesame reference signs. As shown in FIG. 8, the fuel injection controlapparatus includes the controller 30, as well as the crank angle sensor31, the water temperature sensor 33, the intake air amount sensor 34, afuel pressure sensor 36, a fuel temperature sensor 37, and the injector12 that are connected to the controller 30.

The fuel pressure sensor 36 is a sensor that detects the pressure of thehigh-pressure fuel supplied to the injector 12 through a fuel pump andis disposed on, for example, fuel piping. The fuel temperature sensor 37is a sensor that detects the temperature of the fuel supplied to theinjector 12 and is disposed on, for example, fuel piping. The controller30 performs predetermined processing on the basis of signals from thesensors 31, 33, 34, 36, and 37 and outputs controls signals (drivecurrent) to the injector 12 to open the valve of the injector 12.

FIG. 9 is a diagram schematically showing the flow of power supplied tothe injector 12 and shows the flow of power in an inline-four engine,which is an example of the type of the engine 1. In the engine 1, afirst cylinder #1 and a fourth cylinder #4, and a second cylinder #2 anda third cylinder #3 form pairs and are opposed to each other. Thesecylinders are ignited in the order of the first cylinder #1, thirdcylinder #3, fourth cylinder #4, and second cylinder #2 each time thecrank angle is increased by 180°.

As shown in FIG. 9, power (voltage) from a vehicle-mounted battery 41 isboosted by a single booster circuit 42 including a capacitor. Theboosted power is supplied to injectors 12 a to 12 d through a pair ofdriver circuits 43 and 44 as a drive current. Specifically, the drivecurrent is supplied to the injector 12 a of the first cylinder #1 andthe injector 12 d of the fourth cylinder #4 through the driver circuit43 at different timings and is also supplied to the injector 12 b of thesecond cylinder #2 and the injector 12 c of the third cylinder #3through the driver circuit 44 at different timings.

As seen above, the single booster circuit 42 is shared by the fourinjectors 12 a to 12 d and thus the number of booster circuits 42 can bereduced. Also, the pair of driver circuits 43 and 44 are shared by theinjectors 12 a and 12 d and injectors 12 b and 12 c and thus the numberof driver circuits 43 and 44 can be reduced. This allows for a reductionin the number of parts, suppression of the cost, and simplification ofthe configuration.

As shown in FIG. 8, the controller 30 includes, as functional elementsrelated to the drive of the injector 12, the injection mode switchingunit 301, a target injection amount calculation unit 306, an injectiontime calculation unit 307, an injection criterion determination unit308, a crank angle determination unit 309, an injection start time pointcalculation unit 310, and the injector control unit 305.

The target injection amount calculation unit 306 calculates the targetamount of injection per combustion cycle on the basis of the amount ofintake air detected by the intake air amount sensor 34. The targetinjection amount calculation unit 306 also calculates the target amountof one injection (the unit target amount of injection) of the injector12 in accordance with the injection pattern switched by the injectionmode switching unit 301. For example, in the case of two-injectionintake, a value obtained by dividing the target amount of injection percycle by two is calculated as the unit target amount of injection.

The injection time calculation unit 307 calculates the target injectiontime per injection of the injector 12 on the basis of the target amountof one injection (the unit target amount of injection) calculated by thetarget injection amount calculation unit 306, the fuel pressure detectedby the fuel pressure sensor 36, and the fuel temperature detected by thefuel temperature sensor 37. For example, a map representing therelationship among the unit target amount of injection, the fuelpressure, the fuel temperature, and the injection time is previouslystored in the memory, and the target injection time is calculated usingthis map.

The injection criterion determination unit 308 determines which of theinjection start time point and injection end time point should beselected as a reference when the injector 12 injects the fuel, that is,which of the injection start criterion and injection end criterionshould be employed when the injector 12 injects the fuel. Hereafter, forconvenience, a mode in which the injection start time point is selectedas a reference (an injection mode using the start of injection as areference) is referred to as “an injection start priority mode”, and amode in which the injection end time point is selected as a reference(an injection mode using the end of injection as a reference) as “aninjection end priority mode”. FIG. 10A is a diagram showing an exampleof the injection pattern in the injection start priority mode, and FIG.10B is a diagram showing an example of the injection pattern in theinjection end priority mode.

In FIGS. 10A and 10B, a hatched area AR10 centered on the top deadcenter TDC is an injection-prohibited area in which fuel injection isprohibited in a predetermined injection mode. The injection-prohibitedarea AR10 varies among the injection modes, and FIGS. 10A and 10B showexamples of the injection-prohibited area AR10 in the adherencereduction mode M3. A range from the intake top dead center TDC to acrank angle θ11 and a range from a crank angle θ23 to the compressiontop dead center TDC form a range in which the piston crown surface 103 aapproaches the injector 12. In these ranges, the fuel injected from theinjector 12 may adhere to the piston crown surface 103 a and thus sootmay be formed on the piston crown surface 103 a.

For this reason, the range from the intake top dead center TDC to thepredetermined crank angle θ11 and the range from the predetermined crankangle θ23 to the compression top dead center TDC are set as theinjection-prohibited area AR10 so that adherence of soot is prevented.The crank angles θ11 and θ23 defining the injection-prohibited area AR10vary with the engine speed. For example, as the engine speed isincreased, the crank angles θ11 and θ1 are reduced. In FIGS. 10A and10B, the entire range is divided into 30-degree ranges, and the crankangle detected by the crank angle sensor 31 is a multiple of 30°. Theinjection start time point, injection time, and the like are calculatedeach time the crank angle is changed by 30°.

As shown in FIG. 10A, in the injection start priority mode, the fuel isinjected in a crank angle range Δθ11 (θ11 to θ13) corresponding to thetarget injection time calculated by the injection time calculation unit307 from the crank angle θ11 at the injection start time point in theintake stroke. FIG. 10A also shows another crank angle range Δθ10. Thecrank angle range Δθ10 is a reference crank angle range calculated undera steady state, in which the fuel pressure or the like does not vary.The reference crank angle range Δθ10 is determined by the injectionstart crank angle θ11 and the injection time previously estimated undera steady state (reference injection time). In this case, the injectionend crank angle is θ12.

On the other hand, the target injection time calculated by the injectiontime calculation unit 307 is determined in accordance with the fuelpressure, fuel temperature, and the like. Accordingly, the target amountof injection may be longer or shorter than the reference injection time.For example, when the fuel pressure is reduced compared to that in asteady state, the target injection time for injecting the fuel in thetarget amount is increased. As a result, as shown by an arrow A in FIG.10A, the injection end crank angle is increased compared to theinjection end crank angle θ12 in a steady state, that is, becomes θ13(θ12→θ3). In other words, the injection end crank angle deviates fromthe injection end crank angle θ12 in a steady state. However, theinjection start crank angle is θ11 in FIG. 10A, and even if theinjection end time point deviates, the fuel is not injected in theinjection-prohibited area AR10.

On the other hand, if the injection end time point deviates wheninjecting the fuel in the compression stroke, the fuel may be injectedin the injection-prohibited area AR10. For this reason, the injectionstart time point is determined on the basis of the injection endcriterion rather than the injection start criterion, as shown in FIG.10B. Specifically, as shown in FIG. 10B, the fuel is injected using, asthe injection start crank angle, a crank angle θ21 obtained byretreating (decreasing) from the injection end crank angle θ23 by acrank angle range Δθ21 corresponding to the target injection time. FIG.10B also shows another crank angle range 4020. The crank angle range4020 is a reference crank angle range calculated under a steady state,in which the fuel pressure or the like does not vary. The crank anglerange 4020 is determined by the injection end crank angle θ23 and theinjection time previously estimated under a steady state (referenceinjection time). In this case, the injection start crank angle is θ22.

If the fuel injection in the target amount is started from the injectionstart crank angle θ22, that is, if fuel injection is started on thebasis of the injection start criterion, the injection end crank anglemay enter the injection-prohibited area AR10, as shown by a dotted line.On the other hand, if fuel injection is started on the basis of theinjection end criterion, the injection start crank angle is reducedcompared to that in a steady state (θ22→θ21), as shown by an arrow B inFIG. 10B. Thus, the injection start timing is advanced, resulting inprevention of fuel injection in the injection-prohibited area AR10.

The crank angle determination unit 309 determines the crank anglesdefined in accordance with the injection mode, that is, the injectionstart crank angle θ11 and injection end crank angle θ23, as well asdetermines the injection start crank angle in accordance with theinjection criterion determined by the injection criterion determinationunit 308. Specifically, if the injection criterion determination unit308 determines that the fuel should be injected on the basis of theinjection start criterion (injection start priority mode), the crankangle determination unit 309 determines, as the injection start crankangle, the crank angle θ11 (FIG. 10A) determined in accordance with theinjection mode. On the other hand, if the injection criteriondetermination unit 308 determines that the fuel should be injected inaccordance with the injection end criterion (injection end prioritymode), the crank angle determination unit 309 determines, as theinjection start crank angle, the target crank angle θ21 obtained byretreating from the crank angle θ23 (FIG. 10B) determined in accordancewith the injection mode by the crank angle range Δθ21 corresponding tothe target injection time. The crank angle range Δθ21 corresponding tothe target injection time varies with the engine speed.

The injection start time point calculation unit 310 calculates the timepoint at which the actual crank angle θ becomes the injection startcrank angle θ11 or 021 determined by the crank angle determination unit309 (FIG. 10A or 10B), that is, the injection start time point. Whilethe crank angle θ is detected by the crank angle sensor 31 every 30°,the injection start crank angle θ11 or 021 may differ from a crank angleθa (=60°) or θb (=210°), which is a multiple of 30°, detectedimmediately before such a crank angle is detected. For this reason, thetime required for the crank angle θ to move from the crank angle θa orθb to the injection start crank angle θ11 or θ21 is calculated using theengine speed at the time point at which the crank angle θ has become θaor θb, and the injection start time point is calculated on the basis ofthe calculated time.

The injector control unit 305 outputs control signals to the injector 12(more specifically, injector driver circuit) so that the fuel isinjected for the target injection time calculated by the injection timecalculation unit 307 from the injection start time point calculated bythe injection start time point calculation unit 310. Thus, in theinjection start priority mode, the fuel is injected, for example, in arange from the crank angle θ11 to the crank angle θ13 as shown in FIG.10A; in the injection end priority mode, the fuel is injected, forexample, in a range from the crank angle θ21 to the crank angle θ23 asshown in FIG. 10B.

While, as described above, the injection criterion determination unit308 determines which of the injection start time point and injection endtime point should be selected when the injector 12 injects the fuel,that is, determines which of the injection start priority mode andinjection end priority mode should be selected, this determination ismade in accordance with the injection mode switched by the injectionmode switching unit 301. For example, the injection start priority modeis selected in the following first and second cases.

The first case is a case in which the fuel is injected in the intakestroke. Specifically, the first case is a case in which the fuel isinjected by one-injection intake or multi-injection intake in thecatalyst warm-up mode M2, adherence reduction mode M3, or homogeneityimprovement mode M4. If the fuel is injected by multi-injection intake,the first injection is performed in the injection start priority mode.Similarly, if the fuel is injected in the intake stroke and compressionstroke (multiple-injection intake-compression), the first injection isperformed in the injection start priority mode. By injecting the fuel inthe injection start priority mode in the intake stroke as describedabove, injection in the soot formation area (e.g., theinjection-prohibited area AR10 in FIG. 10A) is avoided, resulting inprevention of emission deterioration. Also, formation of a tumble flowin the cylinder 102 is not blocked, allowing the fuel to be injectedafter tumble flow formation. These result in an improvement in thehomogeneity of the mixture and an increase in the combustion efficiency.

The second cases are a case in which the first injection is performedwhen injecting the fuel by multi-injection compression in the start modeM1 and a case in which the fuel is injected in the compression stroke inthe knock suppression mode M5. In particular, by selecting the injectionstart priority mode in the knock suppression mode M5, the fuel isinjected without causing backflow from the intake valve 115 aftersecurely closing the intake valve 115. Thus, the mixture is reliablycooled using the fuel injected from the injector 12, resulting inreliable production of a knocking suppression effect.

On the other hand, the injection end priority mode is selected in thefollowing first and second cases. The first cases include a case inwhich the fuel is injected by single injection in the start mode M1 anda case in which the last injection is performed when injecting the fuelby multi-injection compression stroke in the start mode M1. The firstcases also include a case in which weak stratified combustion isperformed in the catalyst warm-up mode M2, more specifically, a case inwhich the last injection is performed in the compression stroke wheninjecting the fuel by multi-injection intake-compression ormulti-injection compression. By selecting the injection end prioritymode in these cases, fuel injection in the expansion stroke isprevented, resulting in prevention of the fuel from flowing back intothe injector 12 by the pressure of the mixture during combustion. Also,if the driver circuit 43 or 44 is shared by the opposed cylinders (e.g.,first cylinder #1 and fourth cylinder #4) as shown in FIG. 9, onecylinder, #4, is prevented from becoming the fuel injection start timingbefore another cylinder, #1, ends fuel injection. Also, the fuelinjection timing and the ignition timing of the ignition plug 11 areprevented from overlapping each other, resulting in prevention ofadherence of the fuel to the ignition plug 11 from blocking the ignitionof the ignition plug 11.

The second case is a case in which the last injection is performed inthe compression stroke when injecting the fuel by multi-injectionintake-compression, multi-injection compression, or the like in theadherence reduction mode M3. By selecting the injection end prioritymode in this case, injection in the soot formation area (e.g., theinjection-prohibited area AR10 in FIG. 10B) is avoided, resulting inprevention of emission deterioration. Also, if all the injectors 12 a to12 d share the booster circuit 42 as shown in FIG. 9 and if the injector12 a of the first cylinder #1 is driven and then the injector 12 c ofthe third cylinder #3 is driven, issuance of a command to drive theinjector 12 c before the end of drive of the injector 12 a is prevented,allowing the fuel to be reliably injected in the target amount from theinjectors 12 a and 12 c.

FIG. 11 is a flowchart showing an example of a process performed by thecontroller 30 of FIG. 8 in accordance with a program previously storedin the memory. The process shown in this flowchart is started, forexample, when the injection mode is switched to one of the injectionmodes M1 to M5 other than the fuel stop mode M6 of FIG. 4.

As shown in FIG. 11, first, in S21, the controller 30 calculates thetarget amount of injection per combustion cycle on the basis of theamount of intake air detected by the intake air amount sensor 34, aswell as calculates the target amount of one injection (the unit targetamount of injection) of the injector 12 in accordance with the currentinjection mode, which is one of the injection modes M1 to M5. Then, inS22, the controller 30 determines which of the injection start prioritymode and injection end priority mode is the injection priority modecorresponding to the current injection mode, which is one of theinjection modes M1 to M5. If it is determined in S22 that the injectionstart priority mode is the injection priority mode, the process proceedsto S23.

In S23, the controller 30 determines the injection start crank angle(e.g., 011 in FIG. 10A) corresponding to the current injection mode,which is one of M1 to M5. Then, in S24, the controller 30 calculates theinjection start time point corresponding to the injection start crankangle determined in S23, on the basis of the engine speed detected bythe crank angle sensor 31. Specifically, the controller 30 calculatesthe time required to move (increase) from the crank angle θa to theinjection start crank angle θ11 in FIG. 10A and calculates the injectionstart time point on the basis of the calculated time.

Then, in S25, the controller 30 calculates the target injection time onthe basis of the target amount of one injection (the unit target amountof injection) calculated in S21, the fuel pressure detected by the fuelpressure sensor 36, and the fuel temperature detected by the fueltemperature sensor 37. Then, in S26, the controller 30 outputs controlsignals to the injector 12 so that the fuel is injected for the targetinjection time calculated in S25 from the injection start time pointcalculated in S24. Thus, the fuel is injected, for example, in a rangefrom the crank angle θ11 to the crank angle θ13 in FIG. 10A.

On the other hand, if it is determined in S22 that the injection endpriority mode is the injection priority mode, the process proceeds toS27. In S27, the controller 30 determines the injection end crank angle(e.g., 023 in FIG. 10B) corresponding to the current injection mode,which is one of M1 to M5. Then, in S28, the controller 30 calculates thetarget injection time on the basis of the target amount of one injection(the unit target amount of injection) calculated in S21, the fuelpressure detected by the fuel pressure sensor 36, and the fueltemperature detected by the fuel temperature sensor 37.

Then, in S29, the controller 30 calculates a crank angle range (e.g.,Δθ21 in FIG. 10B) corresponding to the target injection time calculatedin S28 on the basis of the engine speed detected by the crank anglesensor 31 and determines, as the injection start crank angle, a crankangle (e.g., 021 in FIG. 10B) obtained by retreating (decreasing) fromthe injection end crank angle determined in S27 by this crank anglerange.

Then, in S30, the controller 30 calculates the injection start timepoint corresponding to the injection start crank angle determined inS29, on the basis of the engine speed detected by the crank angle sensor31. Specifically, the controller 30 calculates the time required to move(increase) from the crank angle θb to the injection start crank angleθ21 in FIG. 10B and calculates the injection start time point on thebasis of the calculated time. Then, the process proceeds to S26, and thecontroller 30 outputs control signals to the injector 12 so that thefuel is injected for the target injection time calculated in S28 fromthe injection start time point calculated in S30. Thus, the fuel isinjected, for example, in a range from the crank angle θ21 to the crankangle θ23 in FIG. 10B.

The present embodiment can achieve advantages and effects such as thefollowing:

(1) The fuel injection control apparatus according to the presentembodiment is formed as a fuel injection control apparatus for theengine 1 including the piston 103 that reciprocates in the cylinder 102and the injector 12 that injects the fuel into the combustion chamber105 facing the piston 103 in the cylinder 102 (FIG. 1). This fuelinjection control apparatus includes the intake air amount sensor 34that detects the amount of intake air guided to the cylinder 102; thetarget injection amount calculation unit 306 calculates the targetamount of fuel injected from the injector 12 on the basis of the amountof intake air detected by the intake air amount sensor 34; the injectiontime calculation unit 307 that calculates the target injection time ofthe fuel in accordance with the target amount of injection calculated bythe target injection amount calculation unit 306; the crank angledetermination unit 309 that determines the crank angle defining thestart of injection (e.g., θ11 in FIG. 10A) and the crank angle definingthe end of injection (e.g., θ23 in FIG. 10B); and the injector controlunit 305 that controls the injector 12 so that the fuel is injected inthe injection start priority mode, in which the fuel is injected for thetarget injection time calculated by the injection time calculation unit307 from the injection start time point corresponding to the injectionstart crank angle θ11 determined by the crank angle determination unit309, or the injection end priority mode, in which the fuel is injectedfor the target injection time from the injection start time pointcorresponding to the crank angle (target crank angle) θ21 obtained byretreating from the injection end crank angle θ23 determined by thecrank angle determination unit 309 by the crank angle range Δθ21corresponding to the target injection time calculated by the injectiontime calculation unit 307 (FIG. 8). The injector control unit 305controls the injector 12 so that the fuel is injected in the injectionstart priority mode in the intake stroke and the fuel is injected in theinjection end priority mode in the compression stroke (FIGS. 10A, 10B).Thus, a delay of the injection end time point is prevented fromaffecting the combustion performance.

(2) The injector control unit 305 controls the injector 12 so that thefirst injection is performed in the injection start priority mode wheninjecting the fuel multiple times in the intake stroke (FIG. 10A). Thisprevents fuel injection in the intake stroke-side injection-prohibitedarea AR10 and thus effectively suppresses adherence of soot to thepiston crown surface 103 a or the like.

(3) The injector control unit 305 controls the injector 12 so that thelast injection is performed in the injection end priority mode wheninjecting the fuel multiple times in the compression stroke (FIG. 10B).This prevents fuel injection in the compression stroke-sideinjection-prohibited area AR10 and thus effectively suppresses adherenceof soot to the piston crown surface 103 a or the like.

(4) The fuel injection control apparatus further includes the fuelpressure sensor 36 that detects the pressure of the fuel and the fueltemperature sensor 37 that detects the temperature of the fuel (FIG. 8).The injection time calculation unit 307 calculates the target injectiontime on the basis of the amount of intake air detected by the intake airamount sensor 34, the fuel pressure detected by the fuel pressure sensor36, and the fuel temperature detected by the fuel temperature sensor 37.Thus, the injection start time point is determined in the injection endpriority mode considering the target injection time corresponding to thevariations in the fuel pressure or the like. As a result, the crankangle at which when injection in the target amount is complete isaccurately matched with the injection end crank angle θ23.

(5) As another aspect, the injector control unit 305 controls theinjector 12 so that the first injection is performed in the injectionstart priority mode and the last injection is performed in the injectionend priority mode when injecting the fuel multiple times (for example,by multi-injection intake-compression) in a range from the start of theintake stroke to the end of the compression stroke. Thus, a delay of theinjection end time point is prevented from affecting the combustionperformance.

(6) In this case, the injector control unit 305 controls the injector 12so that the first injection is performed in the intake stroke and thelast injection is performed in the compression stroke. This reliablyprevents injection in the injection-prohibited area AR10 shown in FIGS.10A and 10B.

(7) The fuel injection control apparatus further includes the injectionmode switching unit 301 that switches the injection mode among themultiple injection modes M1 to M5 having different characteristicsrepresenting the injection frequency and injection timing in accordancewith the operation state of the engine 1 (FIGS. 4 and 8). In this case,the injector control unit 305 controls the injector 12 so that the fuelis injected in the injection start priority mode or injection endpriority mode in accordance with the injection mode switched by theinjection mode switching unit 301. Depending on the injection mode,there may be a need to accurately obtain the injection end time point.According to the present embodiment, a delay of the injection end timepoint is prevented from affecting the combustion performance, allowingfor injection at the optimum injection timing corresponding to theinjection mode.

(8) The injection modes switched by the injection mode switching unit301 include the start mode M1, in which the engine 1 is started (FIG.4). When the injection mode switching unit 301 switches the injectionmode to the start mode M1, the injector control unit 305 controls theinjector 12 so that the fuel is injected in the injection end prioritymode. Thus, the injection end timing in the start mode M1 is accuratelydefined, allowing for the optimum start of the engine 1 in the startmode M1.

(9) The start mode M1 is an injection mode in which the fuel is injectedmultiple times, for example, in a range from the start of the intakestroke to the end of the compression stroke. When the injection modeswitching unit 301 switches the injection mode to the start mode M1, theinjector control unit 305 controls the injector 12 so that the firstinjection is performed in the injection start priority mode and the lastinjection is performed in the injection end priority mode. Thus, if thefuel is injected multiple times in the start mode M1, the injectiontiming is optimally controlled.

(10) The injection modes switched by the injection mode switching unit301 include the catalyst warm-up mode M2, in which the exhaust catalystdevice 13 is warmed up (FIG. 4). When the injection mode switching unit301 switches the injection mode to the catalyst warm-up mode M2, theinjector control unit 305 controls the injector 12 so that the fuel isinjected in the injection end priority mode. Thus, the injection endtiming in the catalyst warm-up mode M2 is accurately defined, allowingfor optimum warm-up of the catalyst device 13 in the catalyst warm-upmode M2.

(11) The injection modes switched by the injection mode switching unit301 include the adherence reduction mode M3, in which the inside of thecylinder 102 is warmed up (FIG. 4). The adherence reduction mode M3 isan injection mode in which the fuel is injected multiple times in arange from the start of the intake stroke to the end of the compressionstroke. When the injection mode switching unit 301 switches theinjection mode to the adherence reduction mode M3, the injector controlunit 305 controls the injector 12 so that the first injection isperformed in the injection start priority mode and the last injection isperformed in the injection end priority mode. Thus, fuel injection inthe injection-prohibited area AR10 is prevented, resulting in favorablesuppression of adherence of soot to the piston crown surface 103 a.

(12) The injection modes switched by the injection mode switching unit301 include the homogeneity improvement mode M4, in which the fuel isinjected only in the intake stroke after warm-up of the inside of thecylinder 102 (FIG. 4). When the injection mode switching unit 301switches the injection mode to the homogeneity improvement mode M4, theinjector control unit 305 controls the injector 12 so that the fuel isinjected in the injection start priority mode. Thus, the injection starttiming in the homogeneity improvement mode M4 is accurately defined,allowing for optimum operation of the engine 1 in the homogeneityimprovement mode M4.

(13) The injection modes switched by the injection mode switching unit301 include the knock suppression mode M5, in which the fuel is injectedin the intake stroke and compression stroke such that knocks aresuppressed (FIG. 4). When the injection mode switching unit 301 switchesthe injection mode to the knock suppression mode M5, the injectorcontrol unit 305 controls the injector 12 so that the fuel is injectedin the injection start priority mode in the compression stroke. Thus,the fuel is injected without causing backflow from the intake valve 115after securely closing the intake valve 115, allowing for optimumoperation of the engine in the knock suppression mode M5.

In the above embodiment, the injector control unit 305 serving as aninjector control unit controls the injector 12, for example, so that thefuel is injected in the injection start priority mode (a first injectionmode) in the intake stroke and the fuel is injected in the injection endpriority mode (a second injection mode) in the compression stroke. Inanother aspect, the injector control unit 305 controls the fuel injectorso that the first injection is performed in the injection start prioritymode (a first injection mode) and the last injection is performed in theinjection end priority mode (a second injection mode) when injecting thefuel multiple times in a range from the start of the intake stroke tothe end of the compression stroke. In yet another aspect, the injectorcontrol unit 305 controls the injector 12 so that the fuel is injectedin the injection start priority mode (a first injection mode) orinjection end priority mode (a second injection mode) in accordance withthe injection mode switched by the injection mode switching unit 301. Asseen above, an injector control unit controls the injector 12 serving asa fuel injector by switching between the injection start priority modeand injection end priority mode in various modes.

While, in the above embodiment, the crank angle determination unit 309determines the crank angle θ11 defining the start of injection (a firstcrank angle) and the crank angle θ23 defining the end of injection (asecond crank angle) in accordance with the injection mode, the firstcrank angle and second crank angle may be determined otherwise. In theabove embodiment, in the injection start priority mode, the fuel isinjected for the target injection time from the injection start timepoint (a first time point) corresponding to the first crank angle θ11determined by the crank angle determination unit 309; in the injectionend priority mode, the fuel is injected for the target injection timefrom the injection start time point (a second time point) correspondingto the crank angle θ21 (a target crank angle) obtained by decreasingfrom the second crank angle θ23 determined by the crank angledetermination unit 309 by the crank angle range Δθ21 corresponding tothe target injection time. While FIG. 10B shows a case in which thecrank angle range Δθ21 is greater than the reference crank angle range4020 calculated under a steady state, the second time point iscalculated also in a case in which Δθ21 is smaller than Δθ20.

While, in the above embodiment, the intake air amount sensor 34 detectsthe amount of intake air, another type of an air amount detector may beused as long as it detects an amount of air flowing into the cylinder ora physical quantity having a correlation with the amount of the air.While, in the above embodiment, the fuel pressure sensor 36 detects thefuel pressure, a pressure detector may be configured otherwise. While,in the above embodiment, the fuel temperature sensor 37 detects the fueltemperature, a temperature detector may be configured otherwise. While,in the above embodiment, the injector 12 serving as a fuel injector ismounted on the cylinder head 104 obliquely downward, the fuel injectormay be configured otherwise as long as it injects the fuel into thecombustion chamber in the cylinder.

While, in the above embodiment, the injection mode switching unit 301switches the injection mode to one of the start mode M1, catalystwarm-up mode M2, adherence reduction mode M3 (cylinder warm-up mode),homogeneity improvement mode M4 (warm-up completion mode), and knocksuppression mode M5 and the fuel is injected in the injection startpriority mode or injection end priority mode in accordance with theswitched injection mode, the fuel may be injected in another injectionmode. That is, the above-mentioned injection modes M1 to M5 are onlyillustrative, and an injection mode switching unit may switch theinjection mode to another injection mode.

The invention can be also configured as a fuel injection control methodfor an internal combustion engine, the internal combustion engineincluding a piston reciprocating in a cylinder and a fuel injectorarranged to inject a fuel into a combustion chamber facing the piston inthe cylinder. Specially, the method includes: detecting an amount of anair flowing into the cylinder or a physical quantity having acorrelation with the amount of the air; calculating a target injectiontime of the fuel including a first target injection time and a secondtarget injection time, based on the amount of the air or the physicalquantity; determining a first crank angle at which a fuel injection bythe fuel injector is to be started and a second crank angle at which thefuel injection is to be ended; controlling the fuel injector so as toinject the fuel in an injection start priority mode in which the fuel isinjected for the first target injection time from a first time pointcorresponding to the first crank angle or an injection end priority modein which the fuel is injected for the second target injection time froma second time point corresponding to a target crank angle, the targetcrank angle being obtained by decreasing a crank angle rangecorresponding to the second target injection time from the second crankangle; and switching an injection mode to one of a plurality ofinjection modes in accordance with an operating state of the internalcombustion engine, an injection frequency and an injection timing beingdetermined in accordance with each of the plurality of injection modes,and wherein the controlling includes controlling the fuel injector so asto inject the fuel in the injection frequency and the injection timingin accordance with the injection mode, and further inject the fuel inthe injection start priority mode or the injection end priority mode inaccordance with the injection mode.

The above embodiment can be combined as desired with one or more of theabove modifications. The modifications can also be combined with oneanother.

According to the present invention, it is possible to be favorablyprevented from affecting a combustion performance due to a delay of aninjection end time point.

Above, while the present invention has been described with reference tothe preferred embodiments thereof, it will be understood, by thoseskilled in the art, that various changes and modifications may be madethereto without departing from the scope of the appended claims.

What is claimed is:
 1. A fuel injection control apparatus for aninternal combustion engine, the internal combustion engine including apiston reciprocating in a cylinder and a fuel injector arranged toinject a fuel into a combustion chamber facing the piston in thecylinder, the apparatus comprising: an air amount detector configured todetect an amount of an air flowing into the cylinder or a physicalquantity having a correlation with the amount of the air; and anelectronic control unit having a microprocessor and a memory, whereinthe microprocessor is configured to perform: calculating a targetinjection time of the fuel including a first target injection time and asecond target injection time, based on the amount of the air or thephysical quantity detected by the air amount detector; determining afirst crank angle at which a fuel injection by the fuel injector is tobe started and a second crank angle at which the fuel injection is to beended; controlling the fuel injector so as to inject the fuel in aninjection start priority mode in which the fuel is injected for thefirst target injection time from a first time point corresponding to thefirst crank angle or an injection end priority mode in which the fuel isinjected for the second target injection time from a second time pointcorresponding to a target crank angle, the target crank angle beingobtained by decreasing a crank angle range corresponding to the secondtarget injection time from the second crank angle; and switching aninjection mode to one of a plurality of injection modes in accordancewith an operating state of the internal combustion engine, an injectionfrequency and an injection timing being determined in accordance witheach of the plurality of injection modes, and wherein the microprocessoris configured to perform the controlling including controlling the fuelinjector so as to inject the fuel in the injection frequency and theinjection timing in accordance with the injection mode, and furtherinject the fuel in the injection start priority mode or the injectionend priority mode in accordance with the injection mode.
 2. Theapparatus according to claim 1, wherein the injection mode includes astart mode in which the internal combustion engine is started, and themicroprocessor is configured to perform the controlling includingcontrolling the fuel injector so as to inject the fuel in the injectionend priority mode when the injection mode is switched to the start mode.3. The apparatus according to claim 2, wherein the fuel is injected in arange from a start of an intake stroke to an end of a compression strokeof the internal combustion engine a plurality of times in the startmode, and the microprocessor is configured to perform the controllingincluding controlling the fuel injector so as to inject the fuel in theinjection start priority mode at a first time and inject the fuel in theinjection end priority mode at a last time in the range when theinjection mode is switched to the start mode.
 4. The apparatus accordingto claim 1, wherein the injection mode includes a catalyst warm-up modein which an exhaust catalyst device disposed on an exhaust passage ofthe internal combustion engine is warmed up, and the microprocessor isconfigured to perform the controlling including controlling the fuelinjector so as to inject the fuel in the injection end priority modewhen the injection mode is switched to the catalyst warm-up mode.
 5. Theapparatus according to claim 1, wherein the injection mode includes acylinder warm-up mode in which an inside of the cylinder is warmed up,the fuel is injected in a range from a start of an intake stroke to anend of a compression stroke of the internal combustion engine aplurality of times in the cylinder warm-up mode, and the microprocessoris configured to perform the controlling including controlling the fuelinjector so as to inject the fuel in the injection start priority modeat a first time and inject the fuel in the injection end priority modeat a last time in the range when the injection mode is switched to thecylinder warm-up mode.
 6. The apparatus according to claim 5, whereinthe injection mode includes a warm-up completion mode in which the fuelis injected in only the intake stroke after a warm-up of the inside ofthe cylinder is complete, and the microprocessor is configured toperform the controlling including controlling the fuel injector so as toinject the fuel in the injection start priority mode when the injectionmode is switched to the warm-up completion mode.
 7. The apparatusaccording to claim 6, wherein the injection mode includes a knocksuppression mode in which the fuel is injected in each of the intakestroke and the compression stroke to suppress an occurrence of aknocking, and the microprocessor is configured to perform thecontrolling including controlling the fuel injector so as to inject thefuel in the injection start priority mode when the fuel is injected inthe compression stroke after the injection mode is switched to the knocksuppression mode.
 8. The apparatus according to claim 1, furthercomprising: a pressure detector configured to detect a pressure of thefuel; and a temperature detector configured to detect a temperature ofthe fuel, wherein the microprocessor is configured to perform thecalculating including calculating the target injection time, based onthe amount of the air or the physical quantity detected by the airamount detector, the pressure of the fuel detected by the pressuredetector, and the temperature of the fuel detected by the temperaturedetector.
 9. A fuel injection control apparatus for an internalcombustion engine, the internal combustion engine including a pistonreciprocating in a cylinder and a fuel injector arranged to inject afuel into a combustion chamber facing the piston in the cylinder, theapparatus comprising: an air amount detector configured to detect anamount of an air flowing into the cylinder or a physical quantity havinga correlation with the amount of the air; and an electronic control unithaving a microprocessor and a memory, wherein the microprocessor isconfigured to function as: an injection time calculation unitcalculating a target injection time of the fuel including a first targetinjection time and a second target injection time, based on the amountof the air or the physical quantity detected by the air amount detector;a crank angle determination unit determining a first crank angle atwhich a fuel injection by the fuel injector is to be started and asecond crank angle at which the fuel injection is to be ended; aninjector control unit controlling the fuel injector so as to inject thefuel in an injection start priority mode in which the fuel is injectedfor the first target injection time from a first time pointcorresponding to the first crank angle or an injection end priority modein which the fuel is injected for the second target injection time froma second time point corresponding to a target crank angle, the targetcrank angle being obtained by decreasing a crank angle rangecorresponding to the second target injection time from the second crankangle; and an injection mode switching unit switching an injection modeto one of a plurality of injection modes in accordance with an operatingstate of the internal combustion engine, an injection frequency and aninjection timing being determined in accordance with each of theplurality of injection modes, and the injector control unit isconfigured to control the fuel injector so as to inject the fuel in theinjection frequency and the injection timing in accordance with theinjection mode switched by the injection mode switching unit, andfurther inject the fuel in the injection start priority mode or theinjection end priority mode in accordance with the injection mode. 10.The apparatus according to claim 9, wherein the injection mode includesa start mode in which the internal combustion engine is started, and theinjection control unit is configured to control the fuel injector so asto inject the fuel in the injection end priority mode when the injectionmode is switched to the start mode by the injection mode switching unit.11. The apparatus according to claim 10, wherein the fuel is injected ina range from a start of an intake stroke to an end of a compressionstroke of the internal combustion engine a plurality of times in thestart mode, and the injection control unit is configured to control thefuel injector so as to inject the fuel in the injection start prioritymode at a first time and inject the fuel in the injection end prioritymode at a last time in the range when the injection mode is switched tothe start mode by the injection mode switching unit.
 12. The apparatusaccording to claim 9, wherein the injection mode includes a catalystwarm-up mode in which an exhaust catalyst device disposed on an exhaustpassage of the internal combustion engine is warmed up, and theinjection control unit is configured to control the fuel injector so asto inject the fuel in the injection end priority mode when the injectionmode is switched to the catalyst warm-up mode by the injection modeswitching unit.
 13. The apparatus according to claim 9, wherein theinjection mode includes a cylinder warm-up mode in which an inside ofthe cylinder is warmed up, the fuel is injected in a range from a startof an intake stroke to an end of a compression stroke of the internalcombustion engine a plurality of times in the cylinder warm-up mode, andthe injection control unit is configured to control the fuel injector soas to inject the fuel in the injection start priority mode at a firsttime and inject the fuel in the injection end priority mode at a lasttime in the range when the injection mode is switched to the cylinderwarm-up mode by the injection mode switching unit.
 14. The apparatusaccording to claim 13, wherein the injection mode includes a warm-upcompletion mode in which the fuel is injected in only the intake strokeafter a warm-up of the inside of the cylinder is complete, and theinjection control unit is configured to control the fuel injector so asto inject the fuel in the injection start priority mode when theinjection mode is switched to the warm-up completion mode by theinjection mode switching unit.
 15. The apparatus according to claim 14,wherein the injection mode includes a knock suppression mode in whichthe fuel is injected in each of the intake stroke and the compressionstroke to suppress an occurrence of a knocking, and the injectioncontrol unit is configured to control the fuel injector so as to injectthe fuel in the injection start priority mode when the fuel is injectedin the compression stroke after the injection mode is switched to theknock suppression mode by the injection mode switching unit.
 16. Theapparatus according to claim 9, further comprising: a pressure detectorconfigured to detect a pressure of the fuel; and a temperature detectorconfigured to detect a temperature of the fuel, wherein the injectiontime calculation unit is configured to calculate the target injectiontime, based on the amount of the air or the physical quantity detectedby the air amount detector, the pressure of the fuel detected by thepressure detector, and the temperature of the fuel detected by thetemperature detector.
 17. A fuel injection control method for aninternal combustion engine, the internal combustion engine including apiston reciprocating in a cylinder and a fuel injector arranged toinject a fuel into a combustion chamber facing the piston in thecylinder, the method comprising: detecting an amount of an air flowinginto the cylinder or a physical quantity having a correlation with theamount of the air; calculating a target injection time of the fuelincluding a first target injection time and a second target injectiontime, based on the amount of the air or the physical quantity;determining a first crank angle at which a fuel injection by the fuelinjector is to be started and a second crank angle at which the fuelinjection is to be ended; controlling the fuel injector so as to injectthe fuel in an injection start priority mode in which the fuel isinjected for the first target injection time from a first time pointcorresponding to the first crank angle or an injection end priority modein which the fuel is injected for the second target injection time froma second time point corresponding to a target crank angle, the targetcrank angle being obtained by decreasing a crank angle rangecorresponding to the second target injection time from the second crankangle; and switching an injection mode to one of a plurality ofinjection modes in accordance with an operating state of the internalcombustion engine, an injection frequency and an injection timing beingdetermined in accordance with each of the plurality of injection modes,and wherein the controlling includes controlling the fuel injector so asto inject the fuel in the injection frequency and the injection timingin accordance with the injection mode, and further inject the fuel inthe injection start priority mode or the injection end priority mode inaccordance with the injection mode.